Because of intensive agriculture, the soils are always in need of soil amendments to modify their chemical, physical and/or biochemical properties and to feed the cultivated plants. Indeed, every season, plants draw from the soil the nutrients they need to grow. Soil amendments are therefore needed to put back into the soil the nutrients that the next crop will require and optimize the soil's physical, chemical and biochemical characteristics.
Soil amendments, also called soil conditioners, are materials added to soil to improve plant growth and health. Generally speaking, a soil amendment is any material added to a soil to improve its physical, biochemical or chemical properties. The type of amendment added depends on the current soil composition, climate and the type of plant. Some soils lack nutrients necessary for proper plant growth and others hold too much or too little water. An amendment or a combination of amendments corrects the soil's deficiencies. The goal is to provide a better environment for roots.
For example, lime is used to make a soil less acidic. Fertilizers, such as peat, manure, anaerobic digestate or compost, add depleted plant nutrients. Materials such as clay, vermiculite, hydrogel and shredded bark will make soil hold more water. Gypsum releases nutrients and improves soil structure. Other soil characteristics that can be modified by an amendment include water retention, permeability, water infiltration, drainage, aeration and structure.
There are two broad categories of soil amendments: organic and inorganic. Organic amendments come from something that is or was alive. Inorganic amendments, on the other hand, are either mined or man-made. Organic amendments include sphagnum peat, wood chips, grass clippings, straw, compost, manure, biosolids, sawdust and wood ash. Traditionally, manure has been used in agriculture as a soil amendment. Compost however is much less used for this purpose because of transport and handling difficulties and costs among others. Inorganic amendments include vermiculite, perlite, tire chunks, pea gravel and sand.
Organic amendments increase soil organic matter content and offer many benefits. Organic matter improves soil aeration, water infiltration, and both water- and nutrient-holding capacity. Many organic amendments contain plant nutrients and act as organic fertilizers. Organic matter also is an important energy source for bacteria, fungi and earthworms that live in the soil.
Some organo-mineral fertilizers, i.e. fertilizers comprising both an organic and an inorganic component, have been described. For example, JP 09132488 describes molded cattle faeces compost, with sawdust, quicklime, and water-absorptive clay mineral prepared by pressure extrusion. PCT application WO 01/13706 describes a pelleted fertilizer comprising specially treated compost and a chemical fertilizer. European patent application 0 597 417 describes a pelleted or granular fertilizer comprising compost and a mineral or organic fertilizer. JP 2000239083 describes a coated fertilizer comprising compost and quicklime. Also, a tribomechanical method for activating the mineral components, and optionally the organic component, in an organo-mineral fertilizer or soil amendment has been described (EP 0 444 392). Fertilizers comprising raw manure have also been described (U.S. Pat. No. 5,741,346). Also, U.S. Pat. No. 6,582,637 presents a compost granulation method.
There is a continuing need for new soil amendments. These amendments may have any of a number of desirable characteristics depending on the type of soil and cultivated plant.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.